Jeff wrote: "Correct. You don't get any better mileage when you use a higher
octane fuel than the truck requires.
And, it take more refining to make a higher octane fuel, and that means it
requires more oil to make a gallon of higher octane fuel than a lower octane
fuel. So you are wasting oil if you are using a higher than need octane
This is correct but incorrect. Additives can put in gasoline to increase
octane ratings. Some work better then others and some are actually more
harmful to the engine or environment. Some have been banned by the federal
government. Lead was a perfect example of a additive that worked good but
was bad for the environment.
To answer Frank's question: Started with low octane regular, if your engine
knocks go to the next grade. Try different brand gasolines. Some vehicles
seemed to run better with different chemical additives to help your engine
run cleaner and more efficient.